[GSBN] Cellulose in unvented roof

[Rob Tom]

On Fri, 11 Jul 2008 13:00:04 -0400, <gsbn-request at greenbuilder.com> wrote:

> Date: Thu, 10 Jul 2008 20:05:15 -0400
> From: "timok" <timok at vitalsystems.net>
> Subject: [GSBN] Cellulose in unvented roof
>
>
> Do any of you have an U.S. building code accepted report or testing on  
> the use of cellulose in an unvented roof cavity.

Tim;

Don't know anything about Murrican Codes/Testing/Reports but about 15  
years ago, Canada Mortgage and Housing Corp  cmhc-schl.gc.ca  did a  
study/report on of a number of houses looking at vented and unvented roofs  
and as one would expect, the unvented roofs were fine.

The issue of course, in not one of whether or not to vent the roof, it's a  
matter of the effectiveness of the air barrier strategy to prevent bulk  
moisture transport via air leakage into the envelope materials.

This would be the case regardless of the type of insulation material used.

Dense-pack cellulose by virtue of it's ... uh... density supposedly allows  
less air movement through the material than other insulations (like say  
fibreglass or wool) but I think that argument is spurious. Cellulose fibre  
insulation is not an effective air barrier material.

The short answer then is --If the air barrier strategy is less than  
effective , then venting the roof cavity is still a Good Thing, especially  
in roof assemblies where there is no attic space.

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at chaffY a h o o  dot  c a >
manually winnow the chaff from my edress in your reply